Process for eliminating delamination between amorphous silicon layers

ABSTRACT

One embodiment is a method of forming a circuit structure. The method comprises forming a first amorphous layer over a substrate; forming a first glue layer over and adjoining the first amorphous layer; forming a second amorphous layer over and adjoining the first glue layer; and forming a plurality of posts separated from each other by removing a first portion of the first amorphous layer and a first portion of the second amorphous layer. At least some of the plurality of posts each comprises a second portion of the first amorphous layer, a first portion of the first glue layer, and a second portion of the second amorphous layer.

This application is a continuation of U.S. patent application Ser. No.12/138,057, filed Jun. 12, 2008, entitled “Process for EliminatingDelamination between Amorphous Silicon Layers,” which claims the benefitof U.S. Provisional Application Ser. No. 61/058,114 filed on Jun. 2,2008, entitled “Process for Eliminating Delamination between AmorphousSilicon Layers,” which applications are hereby incorporated herein byreference in their entireties.

TECHNICAL FIELD

This invention relates generally to integrated circuits, and moreparticularly to methods for forming amorphous silicon layers andelectrodes, and the resulting structures.

BACKGROUND

Spatial light modulators are widely used in commercial products such asvideo displays, televisions, and the like. In general, a spatial lightmodulator includes an array of cells, each of which includes a microminor that can be tilted about an axis and, furthermore, circuitry forgenerating electrostatic forces that operate to tilt the micro mirror.In addition, a spatial light modulator cell typically includesstructures that hold and allow the tilting of the micro mirror. Thereare gaps between the cells for accommodating such structures. Each cellof a spatial light modulator usually further includes stoppers formechanically stopping the cell's micro mirror at the “on” position andthe “off” position, respectively.

In one implementation, for example, in a digital mode of operation fordisplaying video images, there are two positions at which the micromirror can be tilted. In an “on” position or state, the micro minordirects incident light to an assigned pixel of a display. In an “off”position or state, the micro minor directs incident light away from theassigned pixel. The “on” position can be, for example, 20 degrees fromthe horizontal position, and the “off” position can be, for example, 15degrees from the horizontal position.

Spatial light modulators implemented as described above generallyoperate by tilting a selected combination of micro mirrors toselectively project light to display an image on the display. FIG. 1schematically illustrates a spatial light modulator formed on substrate2. The spatial light modulator includes metal post 6, and micro mirror 8residing on metal post 6. Micro minor 8 may be tilted (as shown usingdashed lines) when voltages are applied on metal electrodes 4. Lightthus may be reflected by micro mirror 8 to, or away from, the display(not shown).

The conventional spatial light modulator as shown in FIG. 1 suffers fromdrawbacks. First, the height H of metal post 6 is typically greataccording to the standards of integrated circuit formation processes,and the depositing and patterning of metal post 6 is relativelydifficult. Second, due to the requirements that metal posts/electrodes 6and 4 have different heights, various lithography processes are neededto precisely control the heights of the metal posts/electrodes 6 and 4,again causing an increase in the manufacturing cost. New methods forforming metal posts 6 are thus needed.

SUMMARY OF THE INVENTION

One embodiment is a method of forming a circuit structure. The methodcomprises forming a first amorphous layer over a substrate; forming afirst glue layer over and adjoining the first amorphous layer; forming asecond amorphous layer over and adjoining the first glue layer; andforming a plurality of posts separated from each other by removing afirst portion of the first amorphous layer and a first portion of thesecond amorphous layer. At least some of the plurality of posts eachcomprises a second portion of the first amorphous layer, a first portionof the first glue layer, and a second portion of the second amorphouslayer.

Another embodiment is a method of forming a circuit structure. Themethod comprises forming a first amorphous layer over a substrate;forming a first glue layer over and adjoining the first amorphous layer;forming a second amorphous layer over and adjoining the first gluelayer; and etching the first amorphous layer and the second amorphouslayer in a same process step. A first portion of the first glue layeracts as an etch stop layer.

A further embodiment is a method of forming a circuit structure. Themethod comprises forming a first amorphous layer over a substrate;forming a first glue layer over and adjoining the first amorphous layer;patterning the first glue layer without patterning the first amorphouslayer to form first patterned glue portions; forming a second amorphouslayer over and adjoining the first glue layer; forming a second gluelayer over and adjoining the second amorphous layer; patterning thesecond glue layer without patterning the second amorphous layer to formsecond patterned glue portions; and performing an anisotropic etching toremove amorphous material in the first amorphous layer and the secondamorphous layer using at least some of the first patterned glue portionsand the second patterned glue portions as etch stop layers.

The advantageous features of the present invention include improvedquality of amorphous silicon posts and reduced complexity in forming aplurality of amorphous silicon posts having different heights.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a conventional spatial light modulator including aplurality of metal posts;

FIGS. 2 through 10 are cross-sectional views of intermediate stages inthe manufacturing of an embodiment of the present invention;

FIG. 11 illustrates a spatial light modulator having amorphous siliconposts;

FIGS. 12A and 12B illustrate an inkjet head including amorphous siliconposts;

FIGS. 13A and 13B illustrate a micro flow pump including amorphoussilicon posts;

FIGS. 14A and 14B illustrate a speaker including amorphous siliconposts;

FIGS. 15A and 15B illustrate a microphone including amorphous siliconposts; and

FIGS. 16A and 16B illustrate top views of the amorphous silicon postsshown in FIGS. 11 through 15B.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

A novel method for forming micro posts and the resulting structures areprovided. The intermediate stages of manufacturing a preferredembodiment of the present invention are illustrated. The variations andapplications of the preferred embodiments are then discussed. Throughoutthe various views and illustrative embodiments of the present invention,like reference numbers are used to designate like elements.

Referring to FIG. 2, amorphous silicon layer 22 is formed on substrate20. In an embodiment, substrate 20 includes semiconductor substrate 24,integrated circuit 26 formed at the top surface of semiconductorsubstrate 24, and interconnect structure 28 formed over integratedcircuit 26 and semiconductor substrate 24. Integrated circuit 26 mayinclude CMOS devices, such as NMOS and PMOS devices (not shown).Interconnect structure 28 may include metal lines and vias (refer toFIG. 11, which shows metal lines M1 through M5, and vias Via1 throughVia5) formed in inter-metal dielectric layers. Metal features 30, whichmay be vias or metal pads, are formed at the top surface of substrate20. Through metal features 30 and the underlying metal lines and vias,the subsequently formed amorphous posts 50 (refer to FIGS. 9 and 10) areelectrically connected to integrated circuit 26. In alternativeembodiments, substrate 20 may be a semiconductor or a dielectricsubstrate with no integrated circuit formed therein. For the sake ofsimplicity, in subsequent drawings, integrated circuit 26, interconnectstructure 28, and metal features 30 are not shown.

Amorphous silicon layer 22 is formed on substrate 20 and is electricallyconnected to metal features 30. In an embodiment, amorphous siliconlayer 22 is formed using the commonly used chemical vapor deposition(CVD) methods, such as plasma-enhanced CVD (PECVD). Preferably, when thedeposition proceeds, amorphous silicon layer 22 is in-situ doped with ap-type or n-type impurity to increase its conductivity. Amorphoussilicon layer 22 may also include other elements, such as germanium orthe like. It was found that, if the thickness T of amorphous siliconlayer 22 exceeds a certain value, its quality might be adverselydegraded. For example, if the thickness T is greater than about 6.5 kÅ,the portions of amorphous silicon layer 22 close to the wafer edges maydelaminate. Therefore, the thickness T of amorphous silicon layer 22 ispreferably less than about 6.5 kÅ, and more preferably less than about 6kÅ, and even more preferably between about 2.5 kÅ and about 3.5 kÅ. Oneskilled in the art will realize, however, that the dimensions recitedthroughout the description are merely examples, and will change ifdifferent formation technologies are used. The temperature for formingamorphous silicon layer 22 may be, for example, between about 350° C.and about 400° C.

Since the thickness T of amorphous silicon layer 22 is limited, toachieve a greater thickness T, more than one amorphous silicon layer isstacked to solve the quality degradation problem. Between the formationsteps of the amorphous silicon layers, the formation process is stopped,and the respective wafer comprising substrate 20 may be moved out of thedeposition chamber.

However, the stacking of amorphous silicon layers causes anotherproblem. Experiments performed by the inventors of the presentapplication have revealed that air bubbles may be formed between theamorphous silicon layers. To solve this problem, in the embodiments ofthe present invention, glue layers are formed between amorphous siliconlayers. Referring to FIG. 3, glue layer 34 is formed on amorphoussilicon layer 22. In an embodiment, glue layer 34 is formed of titanium,titanium nitride, tantalum, tantalum nitride, compounds thereof,multi-layers thereof, or the like. In other embodiments, any othermaterials that can glue two amorphous silicon layers without causingbubbles and are at least semi-conductive may be used. Glue layer 34 mayhave a thickness of between about 0.5 kÅ and about 2.0 kÅ. The formationmethod of glue layer 34 is physical vapor deposition (PVD).

FIG. 4 illustrates the patterning of glue layer 34 to form glue layerpatterns 36, which may be performed, for example, by dry etching. Gluelayer patterns 36 are separated from each other. The locations anddimensions of glue layer patterns 36 are determined by the requirementsof the respective applications. Next, as shown in FIG. 5, amorphoussilicon layer 38 is formed, followed by the formation of glue layer 40.The formation processes and the dimensions of amorphous silicon layer 38and glue layer 40 may be essentially the same as the formation ofamorphous silicon layer 22 and glue layer 34 (refer to FIG. 3),respectively. Glue layer 40 may be formed of a same material, or of adifferent material selected from a same group of the above-discussedmaterials, as glue layer 34. Alternatively, glue layer 40 is formed of adifferent material than glue layer 34.

Referring to FIG. 6, glue layer 40 is patterned, forming glue layerpatterns 42. The patterns of glue layer patterns 42 may be the same as,or different from, the patterns of glue layer patterns 36. In theillustrated example, glue layer patterns 42 lack a central patternvertically aligned to the central pattern in glue layer patterns 36.

FIGS. 7 and 8 illustrate the formation of amorphous silicon layer 44 andglue layer patterns 48. In FIG. 7, amorphous silicon layer 44 is formed,for example, using essentially the same method as the formation ofamorphous silicon layers 22 and 38. Glue layer 46 is also formed usingessentially the same method, and has similar dimensions and materials,as glue layers 34 and 40 (refer to FIGS. 3 and 5). In FIG. 8, glue layer46 is patterned to form glue layer patterns 48, which may be the sameas, or different from, the patterns of the underlying glue layerpatterns 36 and 42. Although not shown, more amorphous silicon layersmay be stacked on the structure shown in FIG. 8, with glue layers(patterns) formed between the amorphous silicon layers. The desirablenumber of amorphous silicon layers is determined by the required heightof the amorphous silicon posts, as will be discussed in the subsequentparagraphs.

Referring to FIG. 9, the structure as shown in FIG. 8 is etchedanisotropically, for example, by dry etching, to remove the portions ofamorphous silicon un-protected by glue layer patterns 36, 42, and 48.The portions of amorphous silicon underlying glue layer patterns 36, 42,and 48 are not etched, with glue layer patterns 36, 42, and 48 acting asetch stop layers. In the resulting structure, a plurality of amorphoussilicon posts 50 is formed. In an embodiment, the resulting siliconposts 50 all have a same height, which may be formed by making gluelayer patterns 36, 42, and 48 identical to each other. In otherembodiments, amorphous silicon posts 50 have different heights. Thespacings 52 between amorphous silicon posts 50 may be left as airisolations or filled with a dielectric material. The top glue layer onthe top of each of the amorphous silicon posts 50 may be left un-removedin the final structure, as shown in FIG. 9, or may be removed, as shownin FIG. 10.

In the resulting structure as shown in FIG. 9 or FIG. 10, the highestamorphous silicon posts 50 may have a height H′ greater than about 6.5kÅ, and may even be greater than about 10 kÅ. Depending on theapplication, the number, the dimensions, and the locations of amorphoussilicon posts 50 may vary from one application to the next. In anexemplary embodiment, the number of amorphous silicon posts 50 may begreater than about 5. The desirable number of amorphous silicon posts 50is determined by the preferred height of the highest amorphous siliconposts 50, wherein each of the amorphous silicon layers in the amorphoussilicon posts 50 preferably has a thickness of less than about 6.5 kÅ.However, to reduce the manufacturing cost, the thickness of each of theamorphous silicon layers in amorphous silicon posts 50 is preferably notsmaller than, and is preferably greater than, about 3.5 kÅ.

In an embodiment, each of (or at least some of) the amorphous siliconposts 50 is electrically connected to one of underlying metal features30 (refer to FIG. 2). Accordingly, each of the amorphous silicon posts50 may be individually applied with a voltage different from, or thesame as, a voltage applied on other amorphous silicon posts 50.

FIGS. 11 through 15B illustrate application embodiments of the presentinvention. FIG. 11 illustrates a micro minor cell 60 including micromirror 62, which may be formed of metal, over amorphous silicon posts50. In this embodiment, the highest (central) amorphous silicon post 50is placed in the center of micro mirror cell 60, with amorphous siliconposts 50 on both sides of the central amorphous silicon post 50 havingsmaller heights. The micro mirror 62 may be tilted by applyingappropriate voltages on amorphous silicon posts 50. For example, if apositive voltage is applied on the central amorphous silicon post 50, tomake micro minor 62 tilt to the right side, a negative voltage may beapplied on the amorphous silicon posts 50 on the right side of thecentral amorphous silicon post 50. Alternatively, a positive voltage maybe applied on the amorphous silicon posts 50 on the left side of thecentral amorphous silicon post 50. In this case, air isolations 52 areleft to allow space for micro mirror 62 to tilt. In an exemplaryembodiment, the height of the central amorphous silicon post 50 isgreater than about 15 kÅ.

FIGS. 12A and 12B illustrate inkjet head 64, which is used for emittingink. The ink may be stored in storage 68. Inkjet head 64 includes aplurality of amorphous silicon posts 50, with the central amorphoussilicon post 50 being lower than surrounding ones. Conductive membrane66 is attached to the edge ones of the amorphous silicon posts 50. Ifthe amorphous silicon posts 50 directly underlying membrane 66 areapplied with a different voltage than membrane 66, membrane 66 isattracted downward, allowing ink 70 to be stored in inkjet head 64, asis shown in FIG. 12A. When the voltages on the amorphous silicon posts50 directly underlying membrane 66 are reversed, membrane 66 is pushedup, and hence ink 70 is emitted, as shown in FIG. 12B. In this case,spaces 52 are preferably air isolations.

FIGS. 13A and 13B illustrate yet another application, in which amorphoussilicon posts 50 are used in a micro flow pump, which may be used in abio micro electronic mechanic system (MEMS). The embodiment shown inFIGS. 13A and 13B is used to emit fluid 74. The work mechanism issimilar to the embodiment shown in FIGS. 12A and 12B.

FIGS. 14A and 14B illustrate speaker 78, which includes amorphoussilicon posts 50, and conductive membrane 80 attached to edge ones ofthe amorphous silicon posts 50. It is realized that by alternating thevoltages applied on the amorphous silicon posts 50 directly underlyingmembrane 80, membrane 80 may move up and down rapidly, causing thevibration of air, and hence sound is generated. Again, spaces 52 are airisolations.

FIGS. 15A and 15B illustrate microphone 82, which again includesamorphous silicon posts 50 and conductive membrane 84. Amorphous siliconposts 50 may be electrically interconnected, thereby forming a capacitorwith conductive membrane 84. When sound (in the form of air vibration)is received by conductive membrane 84, conductive membrane 84 vibrates,and the distance between conductive membrane 84 and amorphous siliconposts 50 changes, causing the change of the capacitance of therespective capacitor. The sound is thus converted into electricalsignals. In this application, amorphous silicon posts 50 may beseparated from each other by air isolations 52, as shown in FIG. 15A.Alternatively, spacings 52 may be filled with a dielectric material. Inother embodiments, no patterning is performed to separate the gluelayers and amorphous silicon layers into posts, and the resultingstructure is shown in FIG. 15B.

In each of the embodiments shown in FIGS. 11 through 15B, from thecenter going outward, the amorphous silicon posts 50 may form circlessurrounding the central amorphous silicon posts 50, or they may formsquare/rectangle patterns, as shown in the top views of FIGS. 16A and16B, respectively.

The embodiments of the present invention have several advantageousfeatures. The posts are formed of amorphous silicon, and hence thepatterning of the resulting posts is relatively easy, even if the postsmay have great heights. By forming glue layers between amorphous siliconlayers, the heights of the amorphous silicon posts may be increasedwithout causing defects.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1. A method of forming a circuit structure, the method comprising:forming a first amorphous layer over a substrate; forming a firstpatterned glue layer over and adjoining the first amorphous layer;forming a second amorphous layer over and adjoining the first patternedglue layer; and etching the first amorphous layer and the secondamorphous layer in a same process step, wherein a first portion of thefirst patterned glue layer acts as an etch stop layer.
 2. The method ofclaim 1, wherein each of the first amorphous layer and the secondamorphous layer comprises silicon.
 3. The method of claim 1, whereineach of the first amorphous layer and the second amorphous layer has athickness of less than about 6.5 kÅ.
 4. The method of claim 1, whereinthe first patterned glue layer comprises a material selected from thegroup consisting essentially of titanium, titanium nitride, tantalum,tantalum nitride, and a combination thereof.
 5. The method of claim 1further comprising: forming a second patterned glue layer over andadjoining the second amorphous layer; and forming a third amorphoussilicon layer over and adjoining the second patterned glue layer.
 6. Themethod of claim 1, wherein the etching forms a plurality of posts, atleast some of the plurality of posts comprising a portion of the firstamorphous layer, a second portion of the first patterned glue layer, anda portion of the second amorphous layer.
 7. The method of claim 1further comprising removing the first portion of the first patternedglue layer.
 8. A method of forming a circuit structure, the methodcomprising: forming a first amorphous layer over a substrate; forming afirst glue layer over and adjoining the first amorphous layer;patterning the first glue layer without patterning the first amorphouslayer to form first patterned glue portions; forming a second amorphouslayer over and adjoining the first glue layer; forming a second gluelayer over and adjoining the second amorphous layer; patterning thesecond glue layer without patterning the second amorphous layer to formsecond patterned glue portions; and performing an anisotropic etching toremove amorphous material in the first amorphous layer and the secondamorphous layer using at least some of the first patterned glue portionsand the second patterned glue portions as etch stop layers.
 9. Themethod of claim 8, wherein a plurality of posts is formed.
 10. Themethod of claim 9, wherein a first number of the plurality of posts eachdoes not include the second amorphous layer, and a second number of theplurality of posts each includes a portion of the second amorphouslayer.
 11. The method of claim 9, wherein at least one of the pluralityof posts has a different height and a different number of amorphouslayers than other ones of the plurality of posts.
 12. The method ofclaim 8 further comprising removing the at least some of the firstpatterned glue portions and the second patterned glue portions.
 13. Themethod of claim 8, wherein the second patterned glue portions aredirectly above a first number of the first patterned glue portions, andnone of the second patterned glue portions are directly above a secondnumber of the first patterned glue portions.